Losing steps when cutting splines and complex shapes

Hey Guys!
so years ago i acquired an Elu 860 i completely replaced the control system
this is the specifications of the new parts

M760 leadshine Drives - Micro Step Drivers 6 AMP
M0637 stepping motors - NEMA34 Stepper Motors 4.2 AMP 637 oz/in, 1.8 degree, 8 Wires
NES350-36 Power supply output 36VDC ~ 42 VDC,10 AMP, Input 110/230VAC
3 Axis Mach3 USB Motion Card AKZ250 - ECG SAVEBASE
mach3
windows xp machine 2ghz- 512mb ram

ive had a few problems running the machine.

when tuning the motors I cant move them any faster than 100 ipm otherwise the x and y motors stall.
so ive changed the speeds down to a respectable 80ipm and i seemed to solved that issue.

To me, i now have a different issue.
i can jog with no problem. i can cut simple shapes like squares, lines and circles no problem. if i start cutting splines and more complex shapes. the motor stalls and looses its position on the y axis

its infuriating! im unsure of where i should look for this problem. could it be a mach 3 stetting? would more ram help? could it be electrical?. i just dont know!
ive spent the last few weeks trying to solve this issue its driving me crazy. I have a suspicion that it could be one bad connections somewhere, shorting out when lots of current is needed when cutting complex shapes.
Before i completely rewire the machine, i wanted to see what you guys thought. you've always been so helpful in the past.

Any suggestions are welcome.

my apologies if this is in the wrong forum. so many issue didn't know where to put this!!

you time is greatly appreciated.

thanks

Joe

The answer I'd guess is your gearing is wrong (ie new motors different than old motors that presumably the gearing was OK for) ...those motors have good torque in the right rpm range but to top out at 80ipm, I am guessing the gearing is running them too high of an rpm, which is bad for steppers and worse for larger steppers.

I'm not an expert, but just about to look into such issues with a retrofit myself, but posting the current motor rpm that maxes it out and the gearing ratio from motor to movement would get some useful help I'd think.

What type of drive system does the machine have? If screw drive, what is the screw pitch? How big is the machine? Picture?

Those stepper motors have fairly high inductance (13.6mh)to perform well with 42volt power supply.

Try to wire them up as bipolar parallel and set your driver current to 6amps. This will lower the motor inductance to 3.4mh.

If it is already wired up as bipolar parallel, then increase the power supply voltage to 60volts.

What's the leadscrew pitch? I can't find torque curve for your motors but you may be running into the upper limit on how fast the nema34 motor can spin.

Thank you to everyone that has replied. im so grateful.
im at work at the minute and not at my machine. here are the photos that i have access to now.

image of machine
https://www.dropbox.com/s/ingx8r0gew9kh5g/cnc.jpg?dl=0

image of drive system
https://www.dropbox.com/s/wv9d5uk29f...38.49.jpg?dl=0
the motor is at the other end of this view.

this is the old motor image
http://www.cnczone.com/forums/attach...0&d=1311757397

also im 99% sure they are wired bi-polar parallel

gfacer, thankyou for your reply,

im not sure im following exactly what your saying.
Above is an image of the old motors i took off the machine. i definitely over specced the specification of my new parts. they are definitely more powerful that the old motors.
i do not understand how the power of the motors effects the gearing. (please forgive my ignorance, im primarily an operator/programmer, this is my first attempt at rebuilding)
i just assumed those motors being more powerful would just equate to more torque. the drive is definitely an unusual system but is still a lead screw drive. am i getting resonance through this? creating a vibration that then stalls the motor?

thanks

What is the pitch of the screws?

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i just assumed those motors being more powerful would just equate to more torque.

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Steppers are rated for holding torque, when they are not spinning. Yes, bigger motors have more holding torque.
When a stepper starts spinning, the torque starts to decrease. The faster it spins, the less torque it has. Generally, the larger the motor, the faster the torque falls off.
With a fine pitch screw, it's very possible for a small motor to provide better performance than a motor twice it's size, as it may have more torque at higher rpm.

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if i start cutting splines and more complex shapes. the motor stalls and looses its position on the y axis

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Are you running in CV mode?

Does your motion controller have an option for setting the pulse width?

Do you have dual shaft steppers? If you're getting resonance, adding dampers can make a huge difference.

Is there any binding in your system. Remove the motor, and turn the screw with your fingers over the full length of travel. It should be VERY easy to turn. Even the slightest amount of binding can cause steppers to stall.

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Originally Posted by ger21

What is the pitch of the screws?



Steppers are rated for holding torque, when they are not spinning. Yes, bigger motors have more holding torque.
When a stepper starts spinning, the torque starts to decrease. The faster it spins, the less torque it has. Generally, the larger the motor, the faster the torque falls off.
With a fine pitch screw, it's very possible for a small motor to provide better performance than a motor twice it's size, as it may have more torque at higher rpm.




Are you running in CV mode? yes

Does your motion controller have an option for setting the pulse width? yes,

Do you have dual shaft steppers? If you're getting resonance, adding dampers can make a huge difference. yes. how do i know if im getting resonance?

Is there any binding in your system. Remove the motor, and turn the screw with your fingers over the full length of travel. It should be VERY easy to turn. Even the slightest amount of binding can cause steppers to stall.

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Without the motors installed the gantry moves very easily by turning the screw. i don't believe that its binding. especially as it worked with lower powered motors. HOWEVER. when the motors are not installed i can turn the speed of the motors up a lot higher than the 80 ipm. This then leads me to believe it is a binding issue. i really don't believe it is. ive checked the squareness of the machine, ive individually turned each screw through its full length of motion. Neither times have i found issues, i can turn both axis with my little finger (with a wrench connected to the end)

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Neither times have i found issues, i can turn both axis with my little finger (with a wrench connected to the end)

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A wrench gives you a lot more torque than a stepper has. Can you turn the screw with just your fingers easily?

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Originally Posted by ger21

A wrench gives you a lot more torque than a stepper has. Can you turn the screw with just your fingers easily?

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Hey Ger,
im pretty sure its not binding. ive worked on and serviced enough machines to know what that tension feels like.
im certainly not ruling it out. but for now, im not convinced that's the issue.

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Originally Posted by i_am_joe

gfacer, thankyou for your reply,

i just assumed those motors being more powerful would just equate to more torque. the drive is definitely an unusual system but is still a lead screw drive. am i getting resonance through this? creating a vibration that then stalls the motor?

thanks

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Like Jfong said, those motors have a lot of inductance, which limits their responsiveness and speed. Most people focus on the holding torque number, but a motor that's best at holding still isn't necessarily the best at moving quickly. With steppers, you need to look at the torque curve, which charts the torque drop-off as the motor tries to go faster. Motors with high inductance need a correspondingly high voltage to overcome it when rotating at speed. It doesn't sound like your power supply is putting out enough. Using the formula 32 x (square root of the inductance) = max voltage those motors really want up to 118v to perform well. Rewiring them as he suggested will help, assuming your drivers can handle the load. Alternatively, you might try replacing the motors that were originally on those actuators and see if they work any better.

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Originally Posted by awerby

Like Jfong said, those motors have a lot of inductance, which limits their responsiveness and speed. Most people focus on the holding torque number, but a motor that's best at holding still isn't necessarily the best at moving quickly. With steppers, you need to look at the torque curve, which charts the torque drop-off as the motor tries to go faster. Motors with high inductance need a correspondingly high voltage to overcome it when rotating at speed. It doesn't sound like your power supply is putting out enough. Using the formula 32 x (square root of the inductance) = max voltage those motors really want up to 118v to perform well. Rewiring them as he suggested will help, assuming your drivers can handle the load. Alternatively, you might try replacing the motors that were originally on those actuators and see if they work any better.

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Thankyou for your response.
because i was unsure about the motors i should be buying i consulted motiontek (in canada)
i had extensive communication with these guys, i showed them, and told them everything i knew about the machine.

they then specified the parts for me. ( the only thing i sourced separately was the control board)
does this mean that its possible that i do not have the correct combination of parts?.

would a more powerful power supply help the issue?
i do feel somewhat responsible, however i used motiontek for this exact reason. i wanted them to tell me what i needed.

if i have under powered motors that's through what they specified for me.
i certainly don't want to phone, and blame them. but i would expect them to take back the parts and exchange them to something more suitable
.

It's not that they're underpowered. They just may not be a good match for your machine.

If you have them wired bipolar parallel, then they aren't too bad. Just probably larger than you need, which impacts performance.

You still haven't confirmed that they are wired bipolar parallel, and told us what the screw pitch is.